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Small but Significant

Martha’s Vineyard

Transparently Efficient: A cluster of eight subsidized LEED Platinum homes on Martha's Vineyard show that energy use is manageable—and trackable.

September 2011
South Mountain Company

By Nadav Malin

Clustered on a verdant site, the modest-sized houses all have an A-frame design.
Photo © South Mountain Company
Clustered on a verdant site, the modest-sized houses all have an A-frame design.
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Location West Tisbury, Massachusetts (on Martha’s Vineyard)

Gross area 1,250/1,450 ft2 per house (115/135 m2)
Cost $200 per square foot, not including land acquisition, sitework, and the PVs

Completed May 2010

Program Residences

Architect and builder South Mountain Company
Owner Occupants, on land leased from Island Housing Trust

Energy Use


South Mountain Company, an employee-owned design-build firm on Martha’s Vineyard, has lots of experience with energy-efficient, green homes. In approaching this cluster of houses for Island Housing Trust, the firm also had a research agenda: In addition to refining their toolbox of technologies and design solutions for this type of project, they wanted to encourage the occupants to use no more energy than was generated on their rooftops, and they wanted to track how the energy was being used.

The eight homes are split between a 1,250-square-foot two-bedroom model and a 1,450-square-foot three-bedroom model, which is identical to the smaller house except for the addition of an extension for the additional bedroom. They each have a 5 kW photovoltaic array on their south-facing roofs—enough power to make the all-electric homes net energy generators on an annual basis, if the residents are exceptionally frugal.

Each array cost $40,000 and was projected to generate 6,250 kWh per year, but they all generated more than that—beating the prediction by an average of 9 percent. South Mountain’s energy expert Marc Rosenbaum, who authored a report about the homes, credits the high-quality SunPower PV systems, but notes that above-average sunlight might also have been a factor.

In pursuit of its research agenda, South Mountain equipped each house with submetering for comfort systems and domestic hot water, including a flow meter on the hot water tank so they could measure both the amount of hot water used and the energy used to heat it. Not surprisingly, the electric resistance water heaters used the most energy of any single system, leading Rosenbaum to suggest that an upgrade to solar hot water or a heat-pump water heater would have been a good additional investment.

Although this was not its first LEED platinum project, South Mountain is not a big fan of the program. “Many clients have asked us to do it,” president John Abrams says, “and we’ve suggested to them to spend their money elsewhere.” These homes also would not have been certified, Abrams says, “except that some very important funding was tied to LEED.”

Once they were committed to doing LEED, however, they didn’t hold back, delivering “Platinum-level certification” where only “certified level” was required. Achieving the Platinum rating took some measures that they found questionable, but Abrams also credits LEED with pushing them on things that they otherwise might have overlooked, such as minimizing the length of hot water distribution runs and actually measuring their job-site waste.

With houses this efficient, the energy bills would be low regardless, so South Mountain upped the ante by offering a prize: Any household that achieved the zero-energy goal in the first year could choose between a $400 gift certificate to a nearby fish market or a share in a local farm’s community-supported agriculture program. Two households proved the goal was achievable and claimed the award.


This article appeared in the September 2011 print issue of GreenSource Magazine.

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